The present invention relates to dynamoelectric machines and, more particularly, to field rotors of large dynamoelectric machines.
One type of large dynamoelectric machine employs a forged rotor of magnetic material into which slots are machined to contain metallic current-carrying field conductors interconnected to produce a desired magnetic flux pattern. The rotor is rotated on an axis to cause the flux pattern to interact with conductors in a stator, whereby electric power is generated in response to rotational torque (in a generator) or a torque is generated in response to input electric energy.
The magnitude of the field flux which may be generated in the rotor is limited by the permissible maximum current in the field conductors. This limit is related to the temperature to which the field windings can be exposed. The maximum current can be increased by providing means for dissipating heat from the windings. One technique for cooling, with which the present invention is concerned, includes flowing a coolant gas in ventilation passages in subslots in the rotor located below the slots containing the windings. Flow channels pass from the subslots radially outward through coolant openings in the windings to dissipate resistive heating losses from the windings.
It is conventional to form a subslot with a smaller cross section than the conductor-containing main slot. A subslot cover between the subslot and the main slot supports the conductors, and other elements above it, provides insulation to ground for the conductors and provides an interface with slot armor lining the main slot.
Machining of rotor slots is complicated by the need to form two slot widths in each slot, namely, the conductor-carrying slot and the narrower subslot. In addition, the subslot cover requires machined holes therein to permit the coolant gas flowing therein to pass from the subslot into the windings. In addition, the requirement that the subslot cover provide an interface between slot armor lining the main slot, as well as electrical insulation to ground, results in a subslot cover having complex geometry and resultant high cost.